Anthracycline antibiotics are useful as antitumor agent and are generally produced by fermentation. For low cost production of anthracyclines, syntheses of the aglycone moiety of the anthracycline compound, anthracyclinone, has also been attempted (see Arcamone "Topics in Antibiotic Chemistry" Vol. 2, pages 99-239 (1978) and Terashima "Journal of Synthetic Organic Chemistry, Japan" 40, 20 (1982)).
The present inventor has now found that when a naphthoquinone or juglone and a furan diene compound of the formula (III) shown later are employed as the starting material and condensed, the regiospecific Diels-Alder condensation readily proceeds, that the adduct product so obtained from the Diels-Alder reaction can be converted into an acetal compound by the reaction with L-(+)-2,3-butanediol, and that when this acetal compound is condensed with 1-(trimethylsilyl)-2-butanone or 3-methyl-1-(trimethylsilyl)-3-butene-2-on, followed by cyclization of the resultant aldol condensation product, the anthracyclinone skelton can be constructed under stereochemical control. Thus, the present inventor has now first succeeded in achieving practical asymmetric syntheses of the new anthracycline compound of the formula (I) and also anthracyclinone of formula (A) shown below. On the basis of these new findings, this invention has been accomplished.